1. Field of the Invention
The present invention generally relates to a packet transmission device and a packet transmission system each of which realizes communication by exchanging packets as basic units of the communication, and, more particularly, to a packet transmission device and a packet transmission system each of which uses IP packets, which are used in communication by using the Internet Protocol (IP). The packet transmission device and the packet transmission system are applicable to an IP network, and are used to connect IP routers located in different places.
2. Description of the Related Art
Recently, WDM (Wavelength Division Multiplexing) transmission technologies are becoming widely available for the purpose of heavily increasing network capacity. In addition, the WDM transmission technologies are becoming available for transmitting IP packets. Conventionally, in order to transmit an IP packet by using the WDM transmission technologies, it is required to map the IP packet into an SDH (Synchronous Digital Hierarchy) path first, and then a SDH path signal needs to be transmitted by a WDM transmission signal. Therefore, in order to transmit an IP packet by using the WDM transmission technologies, as shown in FIG. 18, packet transmission devices 1,3,5 and SDH transmission devices 7,9 are necessary.
As to other methods for transmitting the IP packet, an ISDN (Integrated Services Digital Network) and a leased line are widely used. For realizing a high-capacity transmission of the IP packet, an IP packet transmission device which implements a technology called IP-over-SDH, in which technology the IP packet is mapped into an SDH path payload area, is utilized. The IP-over-SDH technologies are completely described in the RFC1619 by the IETF.
In the following, an overview of the IP-over-SDH technologies will be described with reference to FIG. 19 to FIG. 21.
As shown in FIG. 19, IP routers which are located in different places are connected via an SDH transmission network. In the network, IP packets which are assembled in a destination batch are accommodated in an SDH path payload area and an SDH path signal is transmitted. For example, SDH paths are established between an IP router 1201 and each of IP routers 1202-1204.
An SDH signal, which is configured by multiplexing a plurality of SDH path signals, is transmitted over a transmission line from an IP router, and routed in a batch of the SDH path signals at SDH cross-connect devices, and then transmitted to its destination. 7 types of SDH path signals are defined as VC-11, VC-12, VC-2, VC-3, VC-4, VC-4-4c and VC-4-16c (VC is an acronym for Virtual Container). The capacities of the types are 1.6 Mb/s, 2.2 Mb/s, 6.8 Mb/s, 49 Mb/s, 150 Mb/s, 599 Mb/s and 2396 Mb/s respectively. Therefore, if a high-capacity is required between endpoints, VC-3, VC-4, VC-4-4c or VC-4-16c may be used.
An IP router which implements conventional IP-over-SDH technologies generally has a part which processes routing and an interface part for interfacing between the IP router and an outgoing line. The interface part converts IP data into SDH data and converts SDH data into IP data.
A configuration of an IP/STM converter in the interface part will be described with reference to FIG. 20 (STM is an acronym for Synchronous Transport Module). IP packets divided into 3 groups by destinations are entered into IP/VC converters 1331-1333 through IP packet input lines 1301-1303. In the IP/VC converter 1331, first, IP packets are accommodated in an SDH path payload, and second, overhead data entered through an SDH path overhead data input line 1341 and other overhead data generated in the IP/VC converter 1331 are added to the SDH path payload, and, as a result, an SDH path signal, which is called a Virtual Container (VC) signal, is formed and output over an output line 1351. VC signals from the IP/VC converters 1331-1333 are accommodated into an SDH section payload after being multiplexed by a VC multiplexing circuit 1322. An STM signal is formed by adding overhead data to the SDH section payload in an SDH section overhead inserting circuit 1323, and the STM signal is sent out over the line 1311.
In an STM/IP converter, as shown in FIG. 21, first, each VC signal is extracted from an STM signal in an STM/VC converter 1421, and second, IP packets are extracted from SDH path payloads in VC/IP converters 1431-1433. Then the IP packets are sent to the inside of the IP router (1411-13).
As another technology in which packets are accommodated into an SDH section payload area, the international publication W094/03004 (PCT/EP93/01675) xe2x80x9cLocal or/and Transit Exchange for a Broadband Communication Networkxe2x80x9d discloses technologies in which a packet of fixed length (normally called an ATM cell) which is used in an ATM (asynchronous transfer mode) network is accommodated into an SDH section payload area. According to the technologies, the ATM cell is accommodated into the SDH section payload area by way of a VC signal.
However, the above conventional technologies have the following disadvantages. First, in the above conventional WDM technology, because the IP packets should be transmitted via the SDH path, overhead data of the SDH path signal should be transmitted also. Therefore, the transmission capacity of an optical path cannot be fully used, and expensive devices for performing the SDH path transmission are necessary.
Second, in the above conventional IP-over-SDH technology, because the IP packets are transmitted over the SDH path signal, there is an advantage that an IP packet transmission device can transmit the IP packets to a plurality of destinations by connecting one transmission line to the IP packet transmission device. From the viewpoint of the transmission capacity, however, because a part of the transmission capacity is consumed by transmission of the SDH path overhead, the transmission capacity of the transmission line cannot be fully used. Therefore, some problems such as a cost increase of the transmission line may arise for realizing high-capacity communication which is required recently. Further, when the destination of the IP packets is limited to only one, because it is not necessary to have SDH paths, the SDH path overhead area is not used, and, as a result, the overhead part of the transmission capacity is wasted. Further, because an SDH cross-connect system which handles VC-4-4c and/or VC-4-16c is not yet in actual use, it is necessary to establish a plurality of SDH paths between the same endpoints for realizing a high-capacity communication beyond VC-4 (150 Mb/s).
Third, according to the technologies disclosed in the international publication WO94/03004 (PCT/EP93/01675), packets are accommodated into the SDH section payload area by way of VC signal. Therefore, the SDH section payload area should have information used only for handling the VC signal, so a part of the transmission capacity is wasted as in the case mentioned above.
It is a general object of the present invention to provide a packet transmission device and a packet transmission system which can realize high-capacity communication by transmitting packets over a wavelength division multiplexing (WDM) link without any SDH path. It is another object of the present invention to provide a packet transmission device and a packet transmission system which can realize high-capacity communication by eliminating waste of the SDH path overhead area in the case of SDH transmission. It is more specific object of the present invention to provide a packet transmission device and a packet transmission system which is applicable to an IP network.
The above objects of the present invention are achieved by a circuit for converting packets into an optical path signal, wherein the circuit is used in a transmission device for transmitting packets, the circuit including:
a part for converting the packets into a plurality of data streams:
a part for multiplexing the data streams; and
a part for generating the optical path signal by adding at least one overhead to the multiplexed data streams.
The above objects of the present invention are also achieved by a circuit for converting packets into an optical path signal which is used for wavelength division multiplexing (WDM) transmission, wherein the circuit is used in a transmission device for transmitting packets, the circuit including:
a part for converting the packets into a plurality of data streams by using at least one data link layer process;
a part for multiplexing the data streams by using at least one interleaving process and for generating data which is a unit of the wavelength division multiplexing (WDM) transmission; and
a part for generating the optical path signal by adding at least one overhead which is necessary for the wavelength division multiplexing (WDM) transmission to the data.
The above objects of the present invention are also achieved by a circuit for converting an optical path signal into packets, wherein the circuit is used in a transmission device for transmitting packets, the circuit including:
a part for separating at least one overhead from the optical path signal;
a part for generating data streams by demultiplexing data of the optical path signal without the overhead; and
a part for extracting the packets from the data streams.
The above objects of the present invention are also achieved by a circuit for converting an optical path signal which is used for wavelength division multiplexing (WDM) transmission into packets, wherein the circuit is used in a transmission device for transmitting packets, the circuit including:
a part for separating at least one overhead which is necessary for the wavelength division multiplexing (WDM) transmission from the optical path signal;
a part for generating data streams by demultiplexing data of the optical path signal without the overhead; and
a part for extracting the packets from the data streams by using at least one data link layer process.
According to the above inventions, because packets are transmitted directly over the optical path signal and there is no need to establish SDH paths, high-capacity communication can be realized.
The above objects of the present invention are also achieved by a transmission device for transmitting packets, the transmission device including:
a part for converting the packets into an optical path signal and for sending the optical path signal by using wavelength division multiplexing (WDM); and
a part for converting the optical path signal which is received into the packets.
The above objects of the present invention are also achieved by a transmission device for transmitting packets by converting the packets into an optical path signal, the transmission device including:
a packet mapping part for mapping a plurality of packets into an entire payload area of the optical path signal; and
a packet retrieving part for extracting each packet from the payload area.
According to the above inventions, because packets are transmitted directly over the optical path signal and there is no need to establish SDH paths, high-capacity communication can be realized.
The above objects of the present invention are also achieved by a transmission system for transmitting packets, the transmission system including:
a plurality of transmission devices each of which comprises a part for converting the packets into an optical path signal and for sending the optical path signal by using wavelength division multiplexing (WDM), and a part for converting the optical path signal into the packets; and
a part for establishing a connection between said transmission devices by using the optical path signal.
The above objects of the present invention are also achieved by a transmission system for transmitting packets, the transmission system including:
a plurality of transmission devices each of which comprises a packet mapping part for mapping a plurality of packets into an entire payload area of an optical path signal and a packet retrieving part for extracting each packet from the payload area; and
a part for establishing a connection between the transmission devices by using the optical path signal.
According to the above inventions, because packets are transmitted directly over the optical path signal and there is no need to establish SDH paths, high-capacity communication can be realized with low cost.
The above objects of the present invention are also achieved by a circuit for converting packets into a signal which is a transmission unit in a synchronous digital transmission standard, wherein the circuit is used in a transmission device for transmitting packets, the circuit including:
a part for converting the packets into a plurality of data streams;
a part for multiplexing the data streams without adding any overhead for upper layer transmission; and
a part for generating said signal by adding at least one overhead to the multiplexed data streams.
The above objects of the present invention are also achieved by a circuit for converting packets into an STM signal in SDH transmission, wherein the circuit is used in a transmission device for transmitting packets, the circuit including:
a part for converting the packets into a plurality of data streams by using at least one data link layer process;
a part for multiplexing the data streams by using at least one interleaving process without adding any overhead of a VC signal and for generating STM data which is a unit of the SDH transmission; and
a part for generating the STM signal by adding at least one overhead which is necessary for the SDH transmission to the STM data.
The above objects of the present invention are also achieved by a circuit for converting a signal which is a transmission unit in a synchronous digital transmission standard into packets, wherein the circuit is used in a transmission device for transmitting packets, the circuit including:
a part for separating at least one overhead from said signal;
a part for generating data streams by demultiplexing data of the signal without the overhead; and
a part for extracting the packets from the data streams.
The above objects of the present invention are also achieved by a circuit for converting an STM signal in SDH transmission into packets, wherein the circuit is used in a transmission device for transmitting packets, the circuit including:
a part for separating at least one overhead which is necessary for the SDH transmission from the STM signal;
a part for generating data streams by demultiplexing data of the STM signal without the overhead; and
a part for extracting the packets from the data streams by using at least one data link layer process.
According to the above inventions, because packets are mapped directly into the STM signal of SDH, the capacity of a transmission line is used more effectively as compared to the conventional IP-over-SDH, and high-capacity communication can be realized.
The above objects of the present invention are also achieved by a transmission device for transmitting packets, the transmission device including:
a part for converting the packets into a signal which is a transmission unit in a synchronous digital transmission standard and for sending the signal by the synchronous digital transmission; and
a part for converting the signal into the packets.
The above objects of the present invention are also achieved by a transmission device for transmitting packets by converting the packets into an STM signal, the transmission device including:
a packet mapping part for mapping a plurality of packets into an entire section payload area of the STM signal; and
a packet retrieving part for extracting each packet from the section payload area.
The above objects of the present invention are also achieved by a transmission system for transmitting packets, the transmission system including:
a plurality of transmission devices each of which has a part for converting the packets into a signal which is a transmission unit in a synchronous digital transmission standard, a part for sending the signal by the synchronous digital transmission and a part for converting the signal into the packets; and
a part for establishing a connection between the transmission devices by using the signal.
The above objects of the present invention are also achieved by a transmission system for transmitting packets, the transmission system including:
a plurality of transmission devices each of which has a packet mapping part for mapping a plurality of packets into an entire section payload area of an STM signal and a packet retrieving part for extracting each packet from the section payload area; and
a part for establishing a connection between the transmission devices by using the STM signal.
According to the above inventions, because packets are directly mapped into an SDH section payload, waste of the SDH path overhead area can be eliminated. The elimination is effective especially when the destination of the IP packets is limited to only one.
The packets in the above inventions may be IP packets which are used for realizing a communication by the Internet Protocol.
Therefore, according to the present invention, an IP communication network with high-capacity can be realized, and, for example, an intracorporate IP network can be constructed with low cost. Further, carriers can provide high-speed IP communication services with reasonable prices. Furthermore, the present invention may be a solution for the congested traffic in the backbone of the Internet.